High integration in processing a semi-conductor substrate is accompanied with the requirement for a photoresist having a high resolution. However, it is known that a negative type resist composition consisting of a cyclized rubber and a photocrosslinking agent such as hisazide causes swelling during development which results in deteriorating the resolution. In a negative type photoresist composition consisting of a novolak resin and a resolution controlling agent such as naphthoquinonediazide, such swelling does not take place and a high resolution can be obtained. Accordingly, at present, in the fine processing of a semiconductor, a lithography, in which a positive type resist is used, is primarily applied.
The novolak resin, used as a binder, is advantageous because it is soluble in a developing solution without swelling. Further, the novolak resin provides the advantages that it gives a high plasma etching durability to a resist and it enables the development to be carried out in an aqueous alkali. Accordingly, the novolak resin is one of the most desirable binders (these binders are a base component for the resist particularly in the application of the fine processing of a semiconductor).
In the positive type photoresist comprising naphthoquinonediazide and a novolak resin, various attempts on material design have been made in order to obtain a high resolution (resulting in the issuance of many patents and literature discussing such embodiments). For example, it has been found that a naphthoquinonediazide compound provides a dissolution controlling action on the novolak resin and is an important factor for controlling the resolution in the positive type photoresist. This is because the larger this effect is, the larger the dissolution contrast in a development process between an exposed portion and an unexposed portion can be achieved. In recent years, the essence of this dissolution controlling action has been determined to be connected to in the molecular structures of the novolak resin and sensitizer. For example, this dissolution controlling effect is discussed in connection with the molecular structure and physical properties of the novolak resin in the collection of papers from the SPIE Microlithography Symposium, vol. 920, No. 349 and vol. 1262, No. 476 and 493. In addition, many other patents and publications have discussed this connection.
In some cases, in a pattern transfer for processing, the resist used for forming a negative image, rather than a positive image, is desired. Such cases may depend on the kinds of patterns formed and masks. The resist containing a photocrosslinking agent, such as hisazide, is known as a negative type resist in which the novolak resin is used as a binder. However, this resist has the serious defect that because of a narrow latitude in development and a large photoabsorption of the photo-crosslinking agent, the cross-sectional form of the resulting resist pattern shows a reverse trapezoid.
There is available a method in which a photoacid generating agent and an additive (which causes a curing reaction to the binder to occur ( with acid as a catalyst)) are combined and added to the novolak resin to thereby obtain a negative type light-sensitive resin composition. In this method, an increase is expected in the chemical reaction yield (based on a catalytic reaction) following exposure where the addition of a sensitizer results in decreasing the amount of the photoabsorbing component.
Accordingly, it is possible to solve the above problem regarding the cross-sectional form specific to the negative type resist and, therefore, it can be expected to be promising as a resist material for fine processing. Further, because the reaction system is accompanied with an increase in the chemical reaction yield, a high quantum yield, that is, a high sensitivity, can be expected. As a result, the use of this light-sensitive composition for a light-sensitive layer for a lithography can lead to the application to a high sensitivity printing plate suitable for drawing with a laser ray.
The following background art is known for such photocurable resin composition.
That is, there is disclosed in JP-B-54-23574 (the term "JP-B", as used herein, means an examined Japanese patent publication) a technique for photocuring a novolak resin in combination with a photoacid generating agent comprising an organic halogen compound.
It is described in British Patent 1378861 that there can be applied a photoacid generating agent consisting of a diazo compound and a phenol resin such as novolak as a binder for a photocurable composition consisting of methylol melamine and others.
A similar technique is disclosed in U.S. Pat. No. 4,189,323 in which a s-triazine compound having a dinuclear or trinuclear aromatic group is used.
In European Patent 164248 a composition is disclosed comprising an acid curable amino blast resin consisting of a photoacid generating agent, a melamine resin and others, and a conventional novolak resin; and it is described that a negative image can be formed by an aqueous development which has a high heat stability.
In JP-A-62-164045 ( the term "JP-A" as used herein means an unexamined Japanese patent application), an organic halogen compound is disclosed as having photoabsorption in the far UV region which can be favorably used as a photoacid generating agent for such a composition. Similarly, European Patent 349803 describes that an organic halogen compound having a pKa value falling within a specific range is advantageous as a photoacid generating agent of a similar system.
European Patent 361907 discloses that oximesulfonic acid esters are effective as photoacid generating agents for similar photocurable compositions. Further, it is described in U.S. Pat. Nos. 5,057,397 and 5,180,653 that a composition in which a photoacid generating agent having a specific trichlorotriazine group and a novolak resin containing m-cresol of 30% or more in alkoxylated melamine are combined is advantageous for an exposure with high energy rays. Further, it is disclosed in European Patent 397460A that a novolak resin having a high branch degree is used in a similar composition.
In addition, compounds generating a free radical upon decomposition by exposure to light are well known in the field of graphic art. They are widely used as a photopolymerization initiator in a photopolymerizable composition, a photoactivator in a free radical photographic composition, and a photoinitiator in a reaction catalyzed by an acid generated by light. Such a free radical generator is used to prepare various light-sensitive materials in image-forming systems useful for printing, reproduction, copying, etc.
An organic halogen compound is subjected to photodissociation to provide a halogen free radical such as a chlorine free radical and a bromine free radical. These halogen free radicals are good hydrogen-drawing agents and the presence of a hydrogen-providing product generates an acid. The applications thereof to the photopolymerization process and free radical photographic process are described at pages 180 to 181 and 361 to 370 in "Light-Sensitive Systems" written by J. Kosar, John Wiley & Sons (New York 1965).
Carbon tetrabromide, Iodoform and tribromoacetophenone have thus far been representative as the compound generating a halogen free radical by the action of a ray and have been widely used. However, these free radical generators have the defect that they are only decomposed by a ray over a relatively limited wavelength region. That is, they are sensitive in the UV region where the wavelength is shorter than the primary wavelength of a light source commonly used. Accordingly, because of the inability to effectively utilize the rays in the near UV to visible region, these compounds have an inferior ability to generate a free radical.
In order to improve this defect, it was proposed to expand the sensitive wavelength area by adding sensitizers. Such proposed sensitizers were a merocyanine dye, a styryl base and a cyanine dye as described in, for example, U.S. Pat. Nos. 3,106,466 and 3,121,633. The light-sensitive areas of carbon tetrabromide and iodoform are expanded to the visible ray wavelength region. However, it is not yet satisfactory because while the sensitizers having a good compatibility with a free radical generator or the other elements contained in a light-sensitive composition are required to be selected, it is difficult to select those having a good compatibility and showing a high sensitivity.
In order to improve this defect, halogen free radical generators were proposed having a light-sensitive wavelength region extended over a near UV region to a visible ray region. Available are the halomethyl-s-triazine groups described in, for example, U.S. Pat. Nos. 3,954,475, 3,987,037 and 4,189,323. While these compound groups have a light-sensitive wavelength area in the near UV region to the visible ray region, an irradiated ray is not effectively used and the sensitivity for a photodissociation is comparatively low. Further, the light-sensitive compositions in which these triazine compounds are used have the defect that the triazine compound is crystallized during storage for a long period of time, which leads to a reduction in sensitivity.